The present invention relates generally to an image recording apparatus, such as a copying machine, printer. More particularly, the invention relates to an electrophotographic image recording apparatus with a photosensitive drum having a photosensitive surface made of amorphous silicon hydride.
Image recording by way of electrophotographic technique was invented by Carlson and has been extensively used in copying machines and printers. In the electrophotography process, a photosensitive member is uniformly charged by a corotron and is exposed to light to form a latent image thereon. Electrostatically charged fine particles, i.e., toner powders, are applied onto the photosensitive member to be deposited on the latent image by the electrostatic attraction between the latent image and the toner powders, whereby the latent image is developed. In the subsequent step, the toner image is transferred onto a recording medium and is thermally fixed thereon. In the transfer process, a corotron is also disposed at a transfer position.
Amorphous silicon hydride has recently occupied attention as a material for a photosensitive member for its high surface hardness and less wearness in comparison with conventionally used selenium (Se) or cadmium sulfide (CdS). Amorphous silicon hydride may realize a maintenance free photosensitive member, since no substantial wear would occur when it contacts a recording medium or a cleaning brush or blade.
However, in the image recording with the amorphous silicon hydride drum, a first few hundred sheets are printed in pale or blurred form when the printing or recording is resumed after elapse of a considerably long period of time, say more than 10 hours. This phenomenon will be hereinafter be referred to as "initial recording defect" or "initial printing defect". The pale or blurred portion is observed locally of the recording medium, which portion extends in the circumferential direction of the photosensitive drum in the range of from 10 to 20 millimeters and has a width of about three fourth (3/4) with respect to the axial length of the drum. When the image recording is further carried out, the pale or the blurred portion disappears and the entire face of the recording medium is recorded with clear and fine images. Such an initial recording defect does not fail to occur when the image recording is not resumed until more than a certain period of time has elapsed. When the image recording is intermittently carried out with an interval of a certain period of time, the pale or blurred portion tends to spread substantially all over the recording medium.